The present invention relates to a technique for preventing deterioration in positioning accuracy of a magnetic head caused by disturbance. In particular, the present invention is concerned with a magnetic disk drive wherein compensation against disturbance is made by an electronic circuit using sensors.
Magnetic disk drives are required to improve their recording density for increasing their recording capacity. To meet this requirement, it is important how accurately a magnetic head is to be moved to a predetermined position over a magnetic disk medium and allowed to follow a track.
The following are mentioned as factors which impede the positioning accuracy: 1) a slider which carries a magnetic head thereon is influenced by wind created with rotation of a magnetic disk medium, 2) a carriage and another mechanism which support the magnetic head and conduct it to a position over the magnetic disk medium oscillate as a magnetic head positioning operation is performed, and 3) the exertion of an external shock on the magnetic disk drive concerned.
Of these problems, 1) and 2) are concerned with the interior of the magnetic disk drive and could be solved to a certain extent. However, as to 3), it was difficult to solve because it strongly depends on the environment in which the magnetic disk drive is used and the casing, or case, in which it is installed.
In a magnetic disk drive, oscillation generated during seek increases because the access time for stored data is shortened. Under the condition in which plural magnetic disk drives are installed in a case of a server or any other host system, there occurs disturbance in one magnetic disk drive due to operation of the other magnetic disk drive(s).
On the other hand, for the reduction in size and weight of the host system, the rigidity of the case which holds the magnetic disk drives is difficult to be enhanced beyond a certain limit. Thus the conventional oscillation damping effect using an electronic circuit has encountered a limit.
In connection with controlling the positioning of a magnetic head, a technique of detecting an angular acceleration of a mechanical portion (hereinafter referred to as necessary as “Head Disk Assembly” or “HAD”) of a magnetic disk drive and performing feedback of the acceleration to diminish tracking errors caused by shock or oscillation is disclosed, for example, in U.S. Pat. No. 5,426,545 and Japanese Patent Laid-Open No. 2001-291348.
In such a conventional example, for example when a magnetic disk drive is placed on a desk with its widest sides facing up and down, a rotation parameter and gain in a direction running along the desk surface are detected using a sensor and are compensated.
More particularly, in a mode in which the whole of the magnetic disk drive rotates as a rigid body within the desk upper surface, a target track on the magnetic disk medium undergoes a positional displacement according to rotation of the entire magnetic disk drive, whereas an actuator which supports the magnetic head does not rotate due to inertia and tends to stay as it is, with consequent occurrence of a positioning error. This error is compensated in the conventional example, in which, however, consideration is given to only the rotation within the desk upper surface.
There are the following oscillation modes of a magnetic disk drive which occur upon exertion of oscillation on the magnetic disk drive from the exterior. However, it is not that all of the following oscillations are compensated effectively in the prior art.
(1) Thrust Mode of Spindle
In this oscillation mode, an oscillation system using as mass a spindle for rotating a magnetic disk medium and using as spring elements a bearing rigidity in a thrust direction of the spindle and rigidity in a thrust direction of a base is excited by a translational disturbance component acting in a direction perpendicular to the surface of the magnetic disk medium.
(2) Conical Mode of Spindle
This is an oscillation mode in a spindle falling direction in which an oscillation system using an inertia of a spindle as mass and using as a spring element a bearing rigidity in a radial direction of the spindle is excited when a base receives a rotational component of disturbance in an out-of-plane direction of the magnetic disk medium. The “out-of-plane direction” indicates a direction including a component perpendicular to the medium surface (this also applies to the following).
(3) Translation Mode of Spindle
In this oscillation mode, an oscillation system using a spindle as mass and using as a spring element a bearing rigidity in a radial direction of the spindle is excited by a translational disturbance acting in a direction parallel to the surface of the magnetic disk medium. In a spindle of a cantilevered structure, there occurs a flexural deformation of a spindle shaft and therefore a conical mode of the spindle is also excited even by a translational disturbance acting in a direction parallel to the surface of the magnetic disk medium.
(4) In-Plane Rotation Mode Using the Whole of Magnetic Disk Drive as Rigid Body
In this oscillation mode, an oscillation system using as mass a rotational inertia of the whole of a magnetic disk drive and using as a spring element the space between the magnetic disk drive and a case which carries the magnetic disk drive thereon, in a plane of a magnetic disk medium, is excited by another, adjacent magnetic disk drive.